Sulfur compounds, including carbonyl sulfide (“COS”) and carbon disulfide (“CS2”), are typically found in streams derived from gas resources containing carbon dioxide and hydrogen sulfide (“H2S”). The sulfur compounds may be created from CO2 and H2S in refinery processes. Also, the sulfur compounds may be naturally occurring in gas streams produced from reservoirs containing significant quantities of CO2 and H2S.
In various uses for such hydrocarbon streams, existence of the sulfur compounds may have significant detrimental effects. For example, if the hydrocarbon-containing streams are used as feeds for reformers to produce hydrogen-containing streams, the sulfur compounds may “poison” the reforming catalysts. Although the hydrocarbon-containing streams may be scrubbed to remove the CO2 and H2S, the scrubbing processes will not remove all of the sulfur compounds, particularly COS and CS2.
Several known methods may be used to remove COS from the hydrocarbon-containing streams. For example, the COS may be removed by scrubbing with a physical solvent in processes such as the Rectisol® process or scrubbing with a chemical solvents such as diglycol amine (“DGA”). Alternatively, the COS may be removed by absorption onto solid sorbents such as in a Pressure Swing Adsorption (“PSA”) unit. Still other COS removal methods include hydrogenating with hydrogen over a base metal catalyst such as CoMoly and hydrolyzing with water over various specialty catalysts such as catalysts sold under the designations G-41P and C53-2-01 available from Sud Chemie and Puraspec 2312 available from Synetix. All of these known processes are expensive alternatives for removing COS form hydrocarbon-containing streams.
Other processes for removing COS from hydrocarbon-containing streams are known. For example, U.S. Patent Application 2002/0159939 discloses systems for removing odorants and sulfur compounds from gas streams. The systems may include the steps of contacting the stream with a COS hydrolysis catalyst to convert H2S followed by contacting the gas with a material to remove the H2S. Titania, zirconia, thoria, lanthanide oxide, alumina, ceria, molybdenum oxide, vanadium oxide, manganese oxide, cobalt oxide, iron oxide, and nickel oxide are disclosed as a catalyst for hydrolyzing the COS. Zeolites are disclosed as suitable materials for removing the H2S. U.S. Pat. No. 4,735,788 discloses a process for reduction of COS and carbon disulfide compounds in a gas stream containing water vapor through hydrolysis. The catalyst may be titanium dioxide.
PCT Application WO 2004/033367 discloses a variety of processes for removing carbonyl sulfide and carbon disulfide compounds from feeds for hydrogen generators. The processes generally involve a hydrolysis step in which the sulfur compounds are converted to H2S. The processes may also include the use of two solid sorbent beds for removing the sulfur compounds and the hydrogen sulfide. Suitable hydrolysis catalysts are identified as including alumina, zirconia, and titania. Suitable sorbents for removing the H2S are zinc oxide and iron oxide. PCT Application WO 03/011436 discloses a process for removing COS from a stream. The stream is passed through a fixed bed containing both a COS hydrolysis catalyst and a hydrogen sulfide absorbent. The application identifies activated alumina as a suitable hydrolysis catalyst. Suitable H2S absorbents are identified as copper and/or zinc oxides, hydroxides, carbonates, or hydroxycarbonates.